- #26

- 13,433

- 5,950

- B
- Thread starter roineust
- Start date

- #26

- 13,433

- 5,950

- #27

- 13,433

- 5,950

Note that Einstein says: "The question as to whether length contraction

That's what I was trying to tell you in post #22.

- #28

Dale

Mentor

- 29,576

- 5,891

- #29

Ibix

Science Advisor

- 6,446

- 5,144

There is no Planck (or any other) size limit in relativity. My understanding is that the various Planck units are educated guesses for the kind of scale where you need to worry about effects beyond our current best physical models. This does not translate to "there is no concept of time/length/whatever smaller than the Planck one".Doesn't this make either length contraction or Planck size limit not physically real?

- #30

- 296

- 7

Do current particle colliders use enough energy to make the relative size and lifetime of particles smaller than the Planck length & time? If not what are the smallest and shortest scales, that current particle colliders bring particles relative length and lifetime to be?There is no Planck (or any other) size limit in relativity. My understanding is that the various Planck units are educated guesses for the kind of scale where you need to worry about effects beyond our current best physical models. This does not translate to "there is no concept of time/length/whatever smaller than the Planck one".

- #31

- 296

- 7

I've watched the following 3 part video:

If we consider that g=h=c=1 and derive the meter, second and kg from them:

Does length contraction advance at the same rate as time dilation advances, as an object gets closer towards the speed of light?

Is the subject of arbitrariness now still what defines this question, as it was that defined it as originally expressed in this thread?

- #32

- #33

- 296

- 7

How is it that an expression (gamma) that includes time and length in it, in the form of speed, is dimensionless?Either I am misunderstanding your question or it was answered by @PeroK in post #8.

- #34

Dale

Mentor

- 29,576

- 5,891

You can easily work out the units for yourself.How is it that an expression (gamma) that includes time and length in it, in the form of speed, is dimensionless?

- #35

- 13,433

- 5,950

Because it only involves ##v/c## and that is dimensionless.How is it that an expression (gamma) that includes time and length in it, in the form of speed, is dimensionless?

- #36

- 296

- 7

- #37

Nugatory

Mentor

- 12,774

- 5,375

Whatever you mean to say here, it's coming across as nonsense. Try to formulate your question more clearly. If it's a new topic, start a new thread.

- #38

- 13,433

- 5,950

"Dimension" in this context is the physical dimensions of length ##L##, mass ##M## and time ##T##. For example, velocity has dimensions of ##LT^{-1}##,; force has dimensions of ##MLT^{-2}## and energy has dimensions of ##ML^2T^{-2}##.Does a single occurrence of light refraction in water, considered mathematically an addition of a dimension?

This is not to be confused with spatial and time dimensions.

Something like ##\frac v c##, or ##\frac {m_1}{m_2}## which appears in a lot of mechanics problems, is dimensionless. This means also that these quantities are independent of the units. If the velocity is half the speed of light, then ##\frac v c = \frac 1 2## regardless of the units.

See:

https://en.wikipedia.org/wiki/Dimensional_analysis

- #39

- 4

- 0

If you define your unit of length to only rely on your unit of time (which you can do since there is such a well defined, prominent speed...), then it becomes irrelevant what you mean by "1 Second" as well, the ratio still is roughly 2 Planck-Length = 1 Planck-Time. It might be "irrelevant" to ask why - but then, why's that?

- #40

Ibix

Science Advisor

- 6,446

- 5,144

It isn't - your value for the Planck time is off by a factor of roughly two. The Planck time is 5.39×10So why is it only roughly half the length that light could cover in 1 Planck-Time (1*10^-43 s)?

- #41

- 4

- 0

"The **Planck time** is the **time** it would take a photon travelling at the speed of light to across a distance equal to the **Planck length**. " Is the, very sensible, answer to the original question, then. If I had just googled "planck time length" first...this was just such a "1st-post-idiocity" from me, it really made me laugh (and still smile as I type this, in a slightly embarrassed kind of way). Thank you Ibix.

"No. It just means that seconds are bigger than meters."

This just has to be the coolest answer, ever.

"No. It just means that seconds are bigger than meters."

This just has to be the coolest answer, ever.

Last edited:

- Replies
- 5

- Views
- 6K

- Last Post

- Replies
- 5

- Views
- 1K

- Last Post

- Replies
- 5

- Views
- 753

- Last Post

- Replies
- 3

- Views
- 3K

- Last Post

- Replies
- 1

- Views
- 4K

- Replies
- 6

- Views
- 9K

- Last Post

- Replies
- 10

- Views
- 2K

- Last Post

- Replies
- 2

- Views
- 2K

- Last Post

- Replies
- 4

- Views
- 3K

- Last Post

- Replies
- 1

- Views
- 996